The invention relates to a coupling mechanism, in particular for connecting a belt tensioner drive with a belt spool of a belt retractor for a vehicle safety belt.
In order to ensure, in the case of an accident, that the vehicle occupant takes part in the deceleration of the vehicle as early as possible, belt tensioners are often used in connection with the safety belt system. These draw the belt webbing taut and eliminate the so-called belt slack as soon as they are triggered by means of a sensor which is arranged in the vehicle. The belt tensioner engages here on the belt spool by means of a coupling mechanism and sets this belt spool in rotation.
After the end of the action of the belt tensioner and after the vehicle occupant has been stopped by the belt, if possible the normal function of the belt retractor is to be brought about again, so that belt webbing can be unwound, so that the vehicle occupant can move freely.
The coupling mechanism which connects the belt tensioner drive with the belt spool was intended to see to it that on the one hand the belt tensioner in operation is coupled to the belt spool and on the other hand this connection between the belt spool and the belt tensioner is released again after the end of the action of the belt tensioner. For this purpose, the use of various types of coupling is known. For example, grip roller couplings are used, which offer the advantage that they ensure a gentle engagement but have the disadvantage that the disengagement is difficult to produce. On the other hand, pawl couplings are used, which can easily and reliably release the connection with the belt tensioner, but with the engagement process, through the jerky engagement of the pawls, lead to a high stressing of the components of the coupling mechanism.
The invention therefore has the object of providing a coupling mechanism which ensures a gentle engagement of the belt tensioner at the start of the belt tensioning and a reliable disengagement after the tensioning process.
The invention provides a coupling mechanism, in particular for connecting a belt tensioner drive with a belt spool of a belt retractor for a vehicle safety belt, comprising a driving part, an intermediate part, a driven part, a form-fitting coupling and a force-fitting coupling. The form-fitting coupling and the force-fitting coupling are connected in series. The coupling mechanism has an initial state in which the form-fitting coupling is engaged and the force-fitting coupling is disengaged.
In this connection, the term xe2x80x9cinitial statexe2x80x9d designates the state before an accident, i.e. before the actuation of the belt tensioner. In the initial state, the safety belt has the normal retraction- and unwinding function of a conventional belt retractor, belt tensioner and belt retractor are uncoupled. The coupling mechanism of the invention is designed so that it can be used together with a conventional blocking mechanism of a belt retractor. The term xe2x80x9coperating statexe2x80x9d is to be understood as the state during the action of the belt tensioner, in which belt tensioner and belt retractor are coupled with each other. Accordingly, the term xe2x80x9cafter an operationxe2x80x9d designates the state which occurs after the belt tensioner has completed its action; here, the belt tensioner and belt retractor are uncoupled again.
Through the series connection of the two couplings, it is possible to connect the output- and the driving parts with each other by means of the intermediate part, one of the two couplings being respectively arranged between the driving part and the intermediate part or between the driven part and the intermediate part. As in the initial state the form-fitting coupling is engaged and the force-fitting coupling is disengaged, the intermediate piece in the initial state is either connected with the driving part or with the driven part.
The coupling mechanism of the invention combines the advantages of form-fitting and force-fitting coupling types and in so doing avoids the disadvantages thereof, because the reliably disengaging form-fitting coupling is only used for disengagement and the gently engaging force-fitting coupling is only used for engaging. With the transition into the operating state, the force-fitting coupling, which is disengaged in the initial state, is engaged, a gentle engaging being ensured through the use of this type of coupling. The form-fitting coupling is already engaged, so that the abrupt and jerky engaging process of this type of coupling is avoided. In the operating state, both couplings are engaged. Thus the driving part is connected with the driven part via the intermediate part and forms a compact element for the transmission of force from the belt tensioner to the belt spool. After operation, the loosening of the connection between the belt tensioner and the belt spool takes place by the disengaging of the form-fitting coupling which is already engaged in the initial state. Owing to the type of construction of this coupling, the disengagement process takes place in a very reliable manner. The force-fitting coupling, which is complicated to release, remains engaged, After the connection of the belt spool with the belt tensioner is released, the belt spool is freely rotatable again within the framework of the function of a conventional belt retractor.
According to a preferred embodiment, the form-fitting coupling is arranged between the drive- and the intermediate part and the force-fitting coupling is arranged between the intermediate part and the driven part. Thereby, in the initial state, the intermediate part is connected via the form-fitting coupling with the driving part, whereas the belt spool is freely rotatable, because the force-fitting coupling is disengaged. This arrangement offers the advantage that with a radially externally arranged driving part, for accommodating a mechanically costly form-fitting coupling, e.g. a pawl coupling, a large amount of space is available, which reduces the manufacturing expenditure and hence the costs. A form-fitting coupling, e.g. a grip roller coupling, is on the other hand also simple to realize in a confined space. Thus, this arrangement offers the possibility of producing the coupling mechanism at a favorable price.
In particular, it is advantageous if the form-fitting coupling is a pawl coupling. Pawl couplings are easy to realize and ensure a reliable disengagement.
Furthermore, in this advantageous embodiment, provision is made that the force-fitting coupling is a grip roller coupling. Such a coupling ensures a gentle and reliable engagement and a firm connection of the coupled parts.
In an advantageous further development of the invention, holding pins are provided which in the initial state hold the rolling elements of the grip roller coupling and/or the pawls of the pawl coupling in an initial state. This ensures that during the normal operation of the belt retractor in the initial state, the pawl coupling remains engaged and that the grip roller coupling does not engage.
In particular, it is advantageous if the driven part is formed by the axle of the belt spool, because hereby the number of components of the coupling mechanism can be reduced and the manufacturing costs can be made less.
Furthermore, the invention is characterized in that a spring is provided which after operation brings about a rotation of the driven part and thus releases the form-fitting coupling. Advantageously, this spring is the return spring of a belt retractor, so that no additional component has to be provided and thus the expenditure on space and the manufacturing costs can be reduced. As the driving part, e.g. the axle of the belt spool, is connected with the intermediate part via the grip roller coupling, it is thus possible, by means of a rotation of the belt spool, to disengage the pawl coupling between the driving part and the intermediate part and hence to release the connection of the belt spool with the belt tensioner. As a pawl coupling can already be released by a slight rotation, the disengagement mechanism is able to be brought about with minimal effort.
According to another advantageous embodiment of the invention, the force-fitting coupling is arranged between the driving part and the intermediate part and the form-fitting coupling is arranged between the intermediate part and the driven part. Here, it is particularly advantageous if the form-fitting coupling is a claw coupling, because in this way, with a small expenditure in terms of space, a simple and reliable coupling can be created. In this case, in the initial state, the axle of the belt spool is connected with the intermediate part, the axis and intermediate part being freely rotatable with respect to the driving part. The external arrangement of the driving part offers the advantage that a belt tensioner is able to be connected simply therewith.
In this embodiment, furthermore, a spring is provided which after operation moves the intermediate part laterally along the axle of the belt spool and thus releases the form-fitting coupling. Through the displacement of the intermediate part, which is now firmly connected with the driving part, along the axis, the claw coupling, which connects the belt tensioner with the belt spool, can be disengaged in a simple manner.